This mini-lesson covers the CCEA topic Cells: the structure and function of animal, plant and bacterial cells, the jobs of each organelle, how cells become specialised, and how we use a microscope — including how to calculate actual size and magnification.
Work through each screen, answer the questions as you go (some are wordy, some are calculations) and collect ⭐ stars. Press Start when you're ready.
Cells · organelles
Animal & plant cell structure
Both animal and plant cells share five basic parts. A plant cell has all five plus three extras:
Nucleus — controls the cell; contains the DNA (genetic material).
Cytoplasm — jelly where most chemical reactions happen.
Cell membrane — controls what enters and leaves the cell.
Mitochondria — site of aerobic respiration (release energy).
Ribosomes — where protein synthesis happens.
Cell wall (plant) — made of cellulose; supports and strengthens the cell.
Chloroplasts (plant) — contain chlorophyll for photosynthesis.
Permanent vacuole (plant) — filled with cell sap; keeps the cell firm (turgid).
Quick check
Match the function
?A muscle cell needs lots of energy, so it contains very many of one organelle. Which organelle releases energy in aerobic respiration?
Cells · bacteria
Bacterial cell structure
CCEA asks you to compare and contrast bacterial cells with animal and plant cells. A bacterium has a cell wall, cell membrane, cytoplasm and ribosomes, but no true nucleus. Its genetic material is a single loop of DNA in the cytoplasm, and it may carry small extra rings of DNA called plasmids.
Bacterial cell: no true nucleus — a single DNA loop, plus plasmids (extra DNA rings).
Watch out: bacteria do have a cell wall and ribosomes, but the wall is not cellulose, and they have no mitochondria, chloroplasts or true nucleus. Bacteria are also much smaller than animal or plant cells.
Sort it
Whose feature is it?
Tap a feature, then tap the cell type it belongs to. (Some are shared by all.)
🔁 All cells
🌿 Plant only
🦠 Bacteria only
Cells · specialised cells
Specialised cells
In a multi-celled organism, cells become specialised — their structure is adapted to a particular job. The process of a cell developing its specialised features is called differentiation.
Structure suits function: a sperm has a tail and many mitochondria to swim to the egg; a root hair has a long extension to increase surface area for absorbing water; a red blood cell has no nucleus and is packed with haemoglobin to carry oxygen.
Quick check
Why a long tail?
?A sperm cell has a tail and many mitochondria. This is an example of which process making a cell suited to its job?
Cells · microscopy · prescribed practical
Microscopy & magnification
Cells are too small to see with the eye, so we use a light microscope. CCEA expects you to examine and identify cells under a microscope and to calculate the actual size and magnification using a scale bar.
magnification = image size ÷ real sizealso: real size = image size ÷ magnification (rearrange it!)
Prescribed practical: use a light microscope to observe cells and record the magnification.
Worked example — keep units the same!
A cell is really 0.05 mm wide. In a photo it measures 20 mm wide.
magnification = 20 ÷ 0.05 = ×400
Units: 1 mm = 1000 µm and 1 µm = 1000 nm. Always convert both lengths to the same unit before dividing. Magnification is image ÷ real, never real ÷ image.
Calculate
Your turn — magnification
1An onion cell is really 0.1 mm long. Under the microscope its image is 50 mm long. Calculate the magnification.
×
Hint: magnification = image ÷ real = 50 ÷ 0.1.
Calculate
Your turn — find the actual size
2A cell's image is 30 mm wide at a magnification of ×1500. Calculate the actual width of the cell in micrometres (µm). (1 mm = 1000 µm)
µm
Hint: real = image ÷ magnification = 30 ÷ 1500 = 0.02 mm, then × 1000 → µm.
Cells · using a scale bar
Reading a scale bar
Photomicrographs often show a scale bar instead of a magnification. The bar tells you how long a real distance is on the image. You can use it to work out an object's true size.
Worked example — scale bar
A scale bar labelled 10 µm measures 2 mm long on the page (2 mm = 2000 µm).
So 2000 µm on the page = 10 µm real → magnification = 2000 ÷ 10 = ×200.
If a cell measures 40 mm across, its real width = 40 ÷ 200 mm = 0.2 mm = 200 µm.
Tip: measure the scale bar and the object in the same unit, then use the same magnification triangle. The scale bar gives you the magnification; the magnification then gives you any real size.
Calculate
Your turn — from a scale bar
3On a photo, a scale bar labelled 50 µm measures 10 mm long. Calculate the magnification of the photo. (1 mm = 1000 µm, so 10 mm = 10 000 µm)